FIG. 1 is a perspective view of an exemplary medical injection system 100 (the ACIST CVi® system) for delivering a contrast agent into a patient's vascular system for medical imaging. FIG. 1 illustrates a first fluid reservoir 132 for supplying a syringe-type positive displacement pump of a pressurizing unit 130, via a fill tubing line 27-F, and an injection tubing line 27-I coupled to unit 130 for injection of, for example, a radiopaque contrast agent, into a patient's vascular system via an inserted catheter (not shown), for example, coupled to a patient tubing line 122 at a connector 120 thereof. FIG. 1 further illustrates a second fluid reservoir 138 from which a diluent, such as saline, is drawn by a peristaltic pump 106 through yet another tubing line 128 that feeds into tubing line 122. A manifold valve 124 and associated sensor 114 control the flow of fluids into tubing line 122, from pressurizing unit 130 and from tubing line 128.